Constructing a Robust Cathode Electrolyte Interface for Aqueous Hybrid Lithium-Ion Batteries Via Regulating the Solvent–Solute Interaction in a Locally Concentrated Electrolyte

Aqueous lithium-ion batteries have attracted extensive attention as they are low-cost, safe, and environmentally friendly with low-toxicity aqueous electrolytes. The dissolution of transition metals in the cathode material is common in aqueous lithium batteries, leading to a rapid capacity deterioration. However, it is difficult to form an effective cathode electrolyte interface (CEI) layer in an aqueous electrolyte, even in a high-concentration "water in salt" aqueous electrolyte. Herein, a deep eutectic solvent (DES) based on N,N-dimethylacetamide (DMAC), LiClO4, and H2O is proposed as the high-concentrated electrolyte and diluted by nonsolvating 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to obtain a locally concentrated DES aqueous electrolyte. The spectrum analysis and molecular dynamics calculations reveal the enhanced coordination bond strength of Li complexes upon TTE addition. The increased coordination reaction between Li+ and DMAC and the hydrogen bonding between DMAC and H2O profitably forms a robust and uniform CEI on a LiMn2O4 (LMO) cathode, resulting in a hybrid interface composed of a randomly LiF-distributed inner layer and organic outer layer reduced from solvent rather than anion, which can inhibit the Mn dissolution and promote stability of the LMO material effectively. The observation of how the coordination bond strength affects the formed CEI in aqueous electrolyte may provide an insight into more effective interphases of highly stable aqueous batteries.